The invention relates to a decoupling element for use with exhaust-gas systems and with an essentially hollow cylindrical shape with an especially circular or approximately oval cross section, at least consisting of a partially screw-thread-shaped or annular-corrugated bellows and with at least two ends in the form of an inlet and an outlet for the passage of an exhaust gas flow through the decoupling element, wherein a filter element for filtering the exhaust gas flow is arranged at least partially in the interior of the decoupling element.
Such decoupling elements are typically used especially in the field of automotive engineering and are integrated or interconnected in the exhaust-gas system of the engine. In this way, engine movements, as well as vibrations, shocks, and thermal expansions in the exhaust-gas systems due to the exhaust gas flowing out of the engine are absorbed. A portion of the exhaust gases is usually recirculated in a controlled manner into a combustion chamber of the engine. The purpose of this recirculation of exhaust gases is to reduce the combustion temperature in the cylinders of the engine and thus to reduce the formation of nitrogen oxides in the combustion of fuel. For the introduction or recirculation of exhaust gases into the combustion chamber of the engine, in the state of the art, so-called internal and external exhaust-gas recirculation processes are known.
In the case of internal exhaust-gas recirculation, in contrast to external exhaust-gas recirculation that requires a separate recirculation line, the combustion temperature in the cylinders is reduced by increasing the corresponding valve overlap between the intake valve and exhaust valve of each cylinder, so that a portion of the combusted exhaust gases is not ejected from the cylinder. Therefore, the combustion temperature for a new combustion of fuel in the cylinders decreases and a smaller amount of nitrogen oxides is produced.
For reducing the combustion temperature in the cylinders of the engine, external exhaust-gas recirculation is also possible. In the case of external exhaust-gas recirculation, an exhaust-gas line of the exhaust-gas system and an intake system of the engine are connected by an additional exhaust-gas recirculation line arranged outside of the engine. External exhaust-gas recirculation is further differentiated into high-pressure exhaust-gas recirculation (H-EGR) and low-pressure exhaust-gas recirculation (L-EGR). Due to stricter exhaust-gas limits, especially in the case of nitrogen oxides, however, the use of an L-EGR line has increased. If an L-EGR line is used, the removal of the exhaust gas for recirculation into the combustion chamber of the engine takes place downstream of a diesel particulate filter arranged in the exhaust-gas system and the recirculated exhaust gas is introduced into the combustion chamber of the engine typically before a turbocharger or compressor. The exhaust-gas recirculation increases the quantity of the recirculated exhaust gas in the combustion chamber of the engine and reduces the combustion temperature in the combustion chamber in the engine, which finally counteracts the generation of nitrogen oxides in the combustion of fuel.
If an (external) L-EGR line is used, with respect to decoupling oscillations and for compensating for assembly tolerances, correspondingly high requirements compared with internal exhaust-gas recirculation must be satisfied, because additional lines, attachment points, etc. must be used. Another problem in the case of external L-EGR is the release of particles from the diesel particulate filter. These particles are led by the recirculated exhaust gas, first, into the EGR cooler and accumulate in this cooler over time and, second, these particles are introduced upstream of the turbocharger or compressor into the intake system of the main engine and consequently can damage the turbocharger or compressor, as well as pistons and valves of the engine, or can significantly shorten the service life of the turbocharger or compressor or components of the engine.
In the state of the art, it is here already known to guarantee the decoupling of oscillations by a bellows integrated into the L-EGR line, wherein the bellows is typically arranged on the end of the exhaust-gas recirculation line closest to the diesel particulate filter. Also with a high degree of complication, a device is arranged downstream of this bellows in the exhaust-gas recirculation line for separating the particles of the diesel particulate filter named above from the exhaust-gas recirculation flow, in order to prevent damage to the turbocharger, compressor, or components of the engine.
A disadvantage in the state of the art is that the arrangement of an additional particulate separation device in an EGR line is difficult and expensive, because additional joining points are produced and additional parts for the mounting, sealing, etc. are required. Furthermore, the requirements on installation space are also very strict: along the EGR line there must be both the particulate separation device and also a decoupling section for decoupling oscillations. This also causes an increased total weight of the EGR line.
In order to actually be able to perform a particulate separation as well as decoupling along the EGR line, the guidance of the EGR line, the so-called routing, is correspondingly complicated due to the given small installation space. This leads to flow losses in the recirculated exhaust-gas flow and makes the use of economical standard components more difficult. Finally, in the state of the art for particulate separation, typically a non-woven material or a pleated filter is used, wherein the non-woven material is used as a deep-bed filter and the pleated filter is used as a surface filter. The use of a non-woven material and also a pleated filter in a separate housing is also very expensive.
In the state of the art, for example, in DE-A 197 22 603, it is already known to combine a decoupling element for exhaust-gas systems with a filter element in the form of a catalytic converter. Here, the catalytic converter for filtering the exhaust-gas flow is arranged at least partially in the interior of the decoupling element. If this is transferred to the present area of application of the exhaust-gas recirculation, the installation space required for the filtering and decoupling can be reduced, in that the decoupling element, especially the bellows, acts as a housing for the filter element. Simultaneously, the exhaust-gas flow is filtered, so that particles, for example, from an upstream diesel particulate filter, are filtered out from the recirculated exhaust-gas flow and thus an exhaust-gas turbocharger connected before the engine in the direction of flow and also the components of the engine themselves are no longer damaged.
In the European Patent Application EP 1 179 673 A2, a filter element for filtering an exhaust-gas flow is indeed also already disclosed that is integrated in a connection line for the exhaust-gas recirculation. Decoupling or damping of oscillations of the noted connection line from the internal combustion engine is thus not possible, because a corresponding sleeve is provided only for the thermal isolation of the connection line and the intake device of an internal combustion engine from each other at the end of the connection line that is arranged in the region of the intake device of the internal combustion engine.
Due to the reduced installation space of the decoupling element and filter element, the relocation or construction of an L-EGR line is also considerably simplified: not only are fewer individual parts needed for the arrangement and attachment of the L-EGR line, but also standardized, economical line parts or pipes could likewise be used. In addition, flow losses are reduced. Because the filter element is arranged at least partially in the interior of the decoupling element, the weight of the decoupling element and the installed filter element is also significantly less than the sum of the weights of the corresponding individual parts of the state of the art, because a separate filter housing for the filter element can be eliminated.
Such a decoupling element with a filter element can be used universally for different types of engines; only the respective connection pipes must be adapted to corresponding installation-space requirements. The design of the bellows is here adapted to specifications with respect to the desired decoupling effect. Thus, the filter element could be formed as a catalytic converter and, in this way, decoupling and reduction of pollutants both in the non-recirculated exhaust-gas flow and also in the recirculated exhaust-gas flow of the main engine are possible and therefore deposits in the EGR cooler are prevented.